An appropriate neutron source for Boron Neutron Capture Therapy (BNCT) should provide epithermal neutron flux in order of 10 9 n/s.cm 2 . Different neutron sources such as nuclear reactors, different types of accelerators, radioisotopes and neutron generators, have been used in BNCT which have some advantages and disadvantages. The most important of these sources is fission reactors. Reactors have high neutron flux, but they have some disadvantages such as its costs, not portable, lack of possibility to turn on or turn off, radioactive pollution, negative ideas about the safety of reactors. Therefore other neutron sources which have better conditions are interested for BNCT. In this thesis, production of neutron by photoneutron reactions is investigated. For this purpose, electron linear accelerator with energy 510 MeV and current 1.6×10 12 electron per second has been used for Bremsstrahlung radiation. In order to analyze the possibility of using this accelerator for BNCT, production of electrophotons and photoneutrons are simulated by MCNPX code. For this purpose thin and thick targets are analyzed. In thin targets, high energy electrons, produce photons by Bremsstrahlung radiation, then by collision of these photons with second layer as a photoneutron target, neutrons are produced. Tungsten was used as electrophoton target, and cylindrical and half-spherical geometries were investigated. Finally, three optimized electrophoton targets, for maximum photon current, were determined. For Tantalum and Beryllium, and two cylindrical and half-spherical geometries were investigated photoneutron targets. In next step, thick targets were analyzed. In the thick targets, electrophotons and photoneutrons are produced in the same target. In this step, Uranium, Tungsten, Tantalum and Lead were used and cylindrical and half-spherical geometries were investigated. In both stages (thin and thick targets), optimized photoneutron targets for BNCT were chosen base on maximum neutron current, low emission photon pollution, low neutron average energy. Finally, with comparing the optimized targets, thick cylindrical tungsten target with radius 1 cm and thickness 4 cm had the best results for the photoneutrons. This target produce neutron current with 2.73×10 11 n/s which has flux of 8.39×10 9 n/cm 2 .s. The current of emitted photon from this target is 6.11×10 13 p/s and neutron average energy of this target is 1.88 MeV. It seems that this target can provide the needed flux for BNCT. For neutron generator with high intensity based on photoneutron method, high energy and high current electron accelerator need.
